1. Field of the Invention
The present invention relates to an electro-sensitive composition, and in particular to an electro-sensitive composition, the characteristics of which, such as the optical characteristics, viscosity, or the like, can be altered by the application of a voltage.
2. Background Art
Conventionally, electro-sensitive compositions such as electrorheological fluid compositions (hereinbelow referred to as "ER fluid compositions"), liquid crystal compositions, and the like, are known.
An ER fluid composition is a fluid which is obtained by, for example, dispersing solid particles in a medium having electrically insulating properties; such a fluid composition possesses properties such that when a voltage is applied thereto, the viscosity thereof increases; that is to say, such a fluid composition possesses an electrotheological effect (hereinbelow referred to as an "ER effect").
This type of an ER effect is known as a "Winslow Effect"; when such a composition is placed between electrodes and a voltage is applied thereto, the solid particles dispersed in the composition are polarized as a result of the action of the electric field which is generated between the electrodes, and based on this polarization, the solid particles are arranged and linked to one another in the direction of the electric field by means of electrostatic attraction, and an effect of resistance to external shearing flow is exhibited.
As ER fluid compositions exhibit the ER effect described above, it is expected that such fluid compositions will find applications as fluids for braking or power transmission in apparatuses operating by means of electric control, such as clutches, dampers, shock absorbers, valves, actuators, vibrators, printers, vibrating devices, or the like.
Concrete examples of conventionally known ER fluid compositions include fluid compositions in which solid particles having surfaces which absorb and retain water, such as silica gel particles, cellulose particles, starch particles, casein particles, polystyrene-type ion exchange resin particles, or the like, are dispersed in electrically insulating oils such as silicone oil, diphenylchloride, transformer oil, or the like. Furthermore, ER fluids using inorganic solid particles having a low electric conductivity, including semiconductors, as the solid particles (Japanese Patent Application, First Publication, Laid Open No. 2-91194), and ER fluids using inorganic ion exchange particles comprising hydroxides of polyvalent metals, hydrotalcites, acid salts of polyvalent metals, hydroxyapatite, Nashicon (Na ion superionic conductor)-type compounds, clay minerals, potassium titanates, heteropoly acid salts, or insoluble ferrocyanides, as the solid particles (Japanese Patent Application, First Publication, Laid-Open No. 3-200897), are known.
Conventional ER fluid compositions were heterogeneous systems (dispersion systems) in which the solid particles were dispersed in an electrically insulating medium, as explained above, so that in the course of the use or storage, the solid particles tended to condense and precipitate as a result of the attraction therebetween, and to be deposited on electrodes and vessel walls, so that storage stability problems existed which adversely effected the applicability of the ER fluids.
Furthermore, in recent years the use of ER fluid compositions in automobile engines and the like as a lubricating oil has been tested. These tests were based on the idea that, the viscosity of standard lubricating oils declined as the temperature rose, and ER fluid compositions also experienced reduction in viscosity as temperature rose in the same manner in the state in which a voltage was not applied; however, if a voltage was applied to such a fluid, the effect of an increase in viscosity thereby would cancel the decrease in viscosity resulting from the rise in temperature, and as a result, it would be possible to maintain a predetermined viscosity irrespective of temperature.
However, in this case, as well, because the conventional ER fluid compositions were heterogeneous systems containing solid particles, it proved impossible to overcome the problems of abrasion during use as lubricating oils, and such ER fluid compositions thus proved unfit for a practical use.
There was thus a demand for fluid compositions which were homogeneous systems, and moreover were capable of variations in viscosity in response to the application of voltage.
In contrast, liquid crystal compositions are compositions capable of variations in crystal arrangement in a liquid phase as a result of the application of voltage, and as a result of this variation, the optical characteristics thereof are varied. As a result of this characteristic, such liquid crystal compositions have found use primarily as liquid crystal display elements.
Conventional liquid crystal compositions were capable of variation in optical characteristics as a result of the application of a voltage; however, this phenomena was observed only between special electrodes which were disposed with an extremely small gap therebetween and which had the oriented surfaces; furthermore, in order to make this optical variation visible, a complicated structure was required in which polarizing plates or phase contrast plates were incorporated, so that the price thereof was high and accordingly such liquid crystal compositions found use only in small flat plate-type displays.
Thus, a composition capable of variation in optical characteristics without the need of such a complicated structure has been desired.